The proposed investigation is directed toward the synthesis and structural study of new ring containing pentacoordinate phosphate compounds ranging in structure from square pyramidal to trigonal bipyramidal. The results will be used to construct a variable model for the active site of ribonuclease action which involves a pentacoordinated phosphorus intermediate. The limits of the model are to be defined in terms of the energetics introduced by the enzyme constraints on the phosphate moiety. The structures will be established by n.m.r. spectroscopy and, for key members, by X-ray diffraction. Structural perturbations caused by hydrogen bonding, the presence of ring strain, and the presence of hetero atoms will be ascertained in order to refine the model. BIBLIOGRAPHIC REFERENCES: R.R. Holmes, "A Square Pyramidal Model for Ribonuclease Action," Int. J. Peptide and Protein Res., 8, 445, (1976). P.F. Meunier, Joan A. Deiters, and R.R. Holmes, "The Structure of 1,6-Dioxa-4,9 Lambda 5-Phospha-Spiro (4,4) Nonane, (OCH2CH2NH)PH by X-Ray Diffraction and Computer Simulation", Inorg. Chem., 15, Nov. (1976).